1. Field of the Invention
The present invention relates to a traffic flow monitor apparatus for monitoring a traffic flow by using an image received by a TV camera for photographing automobiles running on a road and, more particularly, to a traffic flow monitor apparatus for recognizing a traffic flow while tracking vehicles one by one.
The present invention also relates to a means for detecting a stop state, as a matter of course, and a low-speed running state being free from a stop state on a highway as traffic jam.
2. Description of the Related Art
As a conventional traffic flow monitor apparatus, traffic flow monitor apparatuses described in U.S. Pat. No. 4,847,772, Japanese Unexamined Patent Publication No. 2-166,598, Japanese Unexamined Patent Publication No. 5-298,591, and Japanese Unexamined Patent Publication No. 6-030,417 are known. Of these publications, each of U.S. Pat. No. 4,847,772 and Japanese Unexamined Patent Publication No. 2-166,598 proposes a system in which the image of a road portion on which no vehicle exists is used as a reference image, and, when the luminance distribution of a newly input image is sufficiently different from the luminance distribution of the reference image, it is determined that a vehicle exists on the road portion. On the other hand, each of Japanese Unexamined Patent Publication No. 5-298,591 and Japanese Unexamined Patent Publication No. 6-030,417 proposes a system in which an object detected in a detection area formed on a screen is initially registered as a template, and, subsequently, a vehicle is tracked by correlation calculation to detect traffic jam.
As a conventional traffic flow monitor apparatus, for example, "Examination of Procession Length Measurement Algorithm using Image Processing" (General Meeting of Institute of Electronics and Communication Engineering of Japan: D-423: p.149, 1995) is proposed. In this apparatus, an image is differentiated to check the presence/absence of a vehicle, and the stop of the vehicle is determined on the basis of this frame and the next frame. In this case, when a vehicle exists and is stopped, traffic jam is determined.
In the above related art, in U.S. Pat. No. 4,847,772 and Japanese Unexamined Patent Publication No. 2-166,598, a reference image of a road portion on which no vehicle exists must be registered, and the reference image must be updated depending on a change in shadow or brightness. However, on a crowded road, the registration and updating of the reference image cannot be easily performed, and measurement precision is degraded.
In Japanese Unexamined Patent Publication No. 5-298,591, regardless of the presence/absence of a vehicle, a template having a predetermined size at a predetermined position, i.e., a position spaced apart from a TV camera by a predetermined distance, is registered, and an actual vehicle is tracked. In this system, the size of the template and the size of the actual vehicle are different from each other with movement of the vehicle, and high-precision tracking cannot be performed. In addition, it is difficult to determine whether the shadow of the vehicle or another vehicle which adjacently runs is tracked.
Further, in Japanese Unexamined Patent Publication No. 6-030,417, a plurality of vehicle images are held as templates in advance, and correlation calculation between each image and all the templates is executed each time an image is input. Therefore, in order to obtain a high correlation value, a large number of templates which are different in size, shape, and luminance must be prepared. Therefore, an amount of correlation calculation when the image is input, thereby preventing high-speed processing.
On a highway, when a large number of vehicles run at a low speed, traffic jam must be determined. For this reason, speed measurement is inevitably performed to determine traffic jam. However, in the conventional method, speed measurement cannot be performed, and a vehicle running at a low speed cannot be detected. In the conventional method, movement of a vehicle cannot be detected by the difference between frames for the following reason. That is, even if vehicles run at equal speeds, outputs are different from each other according to the shapes or colors of the vehicles, and outputs are different from each other depending on the distances from a camera.